The problem in the South wasn’t a shortage of blacks to serve on juries, it was that they were actively barred - from juries, voting, lunch counters, bathrooms, drinking fountains, etc. If that’s the case, the problem isn’t the concept of jury nullification.
IIRC, there’s a provision to request a change of venue if the defendant feels the situation in the locale is such that they cannot get a fair trial.
Also, a judge has (I recall seeing it in the news) the option of directing a jury to return “no guilty” or dismissing the charges in that the prosecution has failed to prove the case.
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the classic nullification case (probably repeating myself, not going through 5 pages of posts) is Dr. Henry Morgentaler of Montreal. He was charged with performing an illegal abortion. Apparently he pretty much openly ran a clinic. A jury refused to convict him, the Quebec appeal court substituted a “guilty” verdict.
At the time, the law in Canada had an “out”, abortion was legal if the hospital doctor committee decided it was necessary for the physical or mental health of the mother. As a result, abortion was freely available in some places and impossible in others. Morgentaler thought this was unfair and stupid. the only way they could get a “victim” to testify against him, was to threaten a single African visa student that they would revoke her visa and send her home and tell her family why (where she would likely be killed) if she did not testify about her abortion.
The supreme court of Canada heard the case. The devoutly Catholic minister of Justice, Otto Lang, offered a bet that an appeal court would never nullify a jury verdict again in his lifetime. The Supreme court affirmed the primacy of jury verdicts and said all the appeal court could is order a new trial. In the meantime, he was charged a second time and the jury again acquitted, and the appeal court again substituted a conviction. The retrial, a jury for a third time acquitted.
Eventually, a more progressive government was elected in Quebec and they declined to prosecute him any further.
Eventually, the Supreme Court also affirmed the right to abortion must be more uniform and available country-wide and the current law was unacceptable. So there you go, what was jury nullification one day became perfectly legal the next. The persecution of an obsolete and unfair law was undone mainly because the juries in predominantly Catholic Quebec declined to convict.